1. Field of the Invention
The invention relates generally to a means of improving the production capacity of a gaseous oil well by separating the gas from the crude oil before pumping the oil up the well.
2. Description of the Related Art
When an oil well is initially completed, the downhole pressure may be sufficient to force the well fluid up the well tubing string to the surface. The downhole pressure in some wells decreases, and some form of artificial lift is required to get the well fluid to the surface. One form of artificial lift is suspending an electric submersible pump (ESP) downhole in the tubing string. The ESP will provide the extra lift necessary for the well fluid to reach the surface. In gassy wells, or wells which produce gas along with oil, there is a tendency for the gas to enter the pump along with the well fluid. Gas in the pump decreases the volume of oil transported to the surface, which decreases the overall efficiency of the pump and reduces oil production.
In order to prevent the gas from interfering with the pumping of the oil, various downhole separators have been developed to remove gas from the well fluid prior to the introduction of the fluid into the pump. A typical gas separator is attached to the lower end of the pump assembly, which in turn is suspended on production tubing. Normal gas separators separate most of the gas and discharge the separated gas into the annulus outside the tubing string where the gas flows up the well to the surface. The separator discharges the liquid into the tubing to be pumped to the surface.
A first disadvantage of these separation and pumping systems is that intervention is costly and difficult because the pump assembly is attached to lower end of the tubing string. With the pump assembly attached to the lower end of the tubing string, the well must be xe2x80x9ckilled,xe2x80x9d or the flow of gas and fluid through the perforations is stopped, in order to provide a safe working environment while the tubing string is out of the well. If the well is killed without a means of preventing downward flow, well fluid will flow back into the well where it could be too difficult to retrieve. A second disadvantage of these separation and pumping systems is that all the gas is not always separated from the well fluid, thus a significant portion of the gas may still flow into the pump.
Proposals have been made to suspend the pump assembly and separator on coiled tubing lowered into a liner or casing. However, improvements, particularly for gas separation, are desirable.
The present invention contemplates a means of pumping gas from gassy wells in which the gas is separated before entering the pump by a gas separator located below the pump within a section of a liner or conduit. The pump assembly is lowered into the liner and suspended above the gas separator. There is a set of valves and flow control devices located in the conduit below the pump that allows the pump to be installed and removed while the well is live.
The conduit lands and sealingly engages a packer set in the casing. The conduit has an opening in its lower portion for receiving the gas and well fluid flowing from the perforations in the well. A gas separator is located inside of the conduit for separating gas from the well fluid flowing from the well. The gas that is separated from the well fluid is discharged to an area surrounding the conduit where the gas will flow to the surface. The remaining well fluid is discharged up the conduit.
The pump assembly is made up of a pump, which has an inlet and an outlet, and a motor to drive the pump. The pump assembly lands in the conduit so that the pump and motor are above and not engaged with the gas separator. A pump seal located between the pump and the conduit seals the pump to the conduit when the pump assembly lands in the conduit. The gas separator below the pump separates most of the gas from the well fluid, therefore the pump is more efficient, and can produce more crude oil. The pump outlet is above the pump seal, accordingly the well fluid is discharged into the conduit, above the pump seal, where the fluid flows to the surface.
In the preferred embodiment, there will also be a flow control valve located in the conduit so that the well fluid cannot flow back into well. A circulation valve located above the flow control valve allows circulation from the conduit into the annulus surrounding the conduit. Finally, in the preferred embodiment, a pressure actuated downhole safety valve is located in the conduit to prevent well fluid from flowing up the conduit when it is closed.
In one embodiment of the well, the pump is suspended above the motor, and the pump seal creates a chamber inside of the conduit below the pump seal and above the gas separator. In this embodiment, some of the gas remaining with the well fluid after passing through the gas separator will collect in the chamber. A shroud located below the pump inlet makes it difficult for the remaining gas to enter the pump, so the gas flows past the inlet and collects at the top of the chamber. The remaining gas that collects in the chamber is vented out of the chamber by a vent. In one embodiment, the vent is through the pump seal and opens into the area inside the conduit above the seal. The gas then flows up the conduit to the surface. In another embodiment, the pump assembly is suspended by tubing, and the vent fluidly connects the chamber with the inside of the tubing. In this embodiment the gas flows up the tubing to the surface. In another embodiment, the vent is located in the conduit and discharges the remaining gas to the annulus, where the gas will flow to the surface.
In the final embodiment, the pump is located below the motor, the motor being suspended by a string of coil tubing. In this embodiment, the pump seals engage the conduit when the pump lands in an area of the conduit having a reduced diameter. The gas is separated from the well fluid by the gas separator and discharged into the annulus. The well fluid and some remaining gas flow into the pump inlet, where the fluid and remaining gas are pumped and discharged above the seal to flow to the surface inside the conduit. In this embodiment, there may also be a sand skirt for collecting sand that settles from the fluid flowing to the surface. With any of these embodiments, the pump assembly may be removed for intervention without having to kill the well by closing the safety valve.